For satellites placed at high altitude relative to the Earth (typically above 1000 km), one of the main sources of disturbing torques that might introduce an undesirable modification of the attitude of the satellite is the solar pressure. It is the case for example for satellites placed in geostationary orbit (GEO, altitude of about 36 000 km).
To control the attitude of such a satellite, it is known to use control members allowing to creating reaction torques along three independent axes, for example wheels, such as reaction wheels or flywheels. Such wheels have the advantage of being able to operate using the renewable electrical energy created by solar panels.
However, they must store the angular momentum created by the compensation of some external disturbing torques the mean of which is not zero over a long time period, and this may only be done by progressively increasing the rotation speed of said wheels. These wheels form an angular momentum storage device, and must therefore be de-saturated regularly to reduce their rotation speeds. Without these de-saturation operations, the maximum rotation speeds of the wheels would eventually be attained.
These de-saturation operations are generally performed by means of chemical-propellant thrusters, and consequently give rise to an increased consumption of chemical propellants, this being prejudicial insofar as said chemical propellants are stowed aboard the satellite in necessarily limited quantities.
For satellites comprising solar panels comprising photovoltaic cells, intended to provide the electrical energy necessary for the operation of the satellite payload, it is known to exploit the solar pressure by using said solar panels as a solar sail to de-saturate the wheels. Indeed, it is possible to create torques by skewing the solar panels with respect to the Sun, which torques can be created to modify the attitude of the satellite and/or to de-saturate the wheels.
However, the skewing of the solar panels does not make it possible to create significant torques about the axis of rotation of said solar panels, so that it is not possible to de-saturate the component of the angular momentum of the wheels along this axis of rotation. Moreover, such a skewing of the solar panels gives rise to a sensible decline in the quantity of electrical energy generated by these solar panels.
An exemplary device making it possible to control the attitude of a satellite by using the solar panels while limiting the need for skewing of said solar panels is known from French patent No. 2 530 046. In this example, the solar panels comprise lateral flaps, said flaps exhibiting an inclination of slightly less than 90° with respect to the solar panels. As indicated in said patent, such a device makes it possible to limit the need for skewing of the solar panels insofar as a skewing of a few degrees is sufficient to create suitable torques. However, nor does this device make it possible to create significant torques on the satellite about the axis of rotation of the solar panels, therefore to de-saturate the wheels along this axis.
In the state of the art, the angular momentum created by disturbing torques of non-zero mean along the axis of rotation of the solar panels is accumulated in wheels which are de-saturated by means of chemical-propellant thrusters.